Various measurements need to be taken on a completed power amplifier (PA) to fully characterize the PA and determine that the PA is suitable for service. Those measurements include: input and output power; hot s-parameters (S11, S21, S22); adjacent channel power ratio (ACLR); spectrum emission masks (SEM); error vector magnitude (EVM); and harmonics and spurious measurements (up to about the 5th or 6th harmonic). In addition, the following measurements need to be taken on low power devices under test (DUTs) that makeup part of a PA (power amplifiers, filters, attenuators, and the like): normal (small-signal) s-parameters (s11, s21, s22) and input and output power.
Previous methods of performing the above tests have required either separate setups, where the DUT is connected to first one measuring instrument and then the other, or setups where the DUT is switched between setups, requiring a high-power RF switch at its output. This switch can be a source of unreliability due to the degradation of internal switch contacts when high RF power is run through them and especially in the case where the RF power is switched without momentarily turning it off (“hot switching”).
One previous method found in the Anritsu “PATS” test set has two inherent disadvantages. One disadvantage is that high cost directional couplers at the output of the DUT must pass harmonics up to 13 GHz on its coupled port while handling high power on its through line. Another disadvantage is that the small-signal s22 and “hot” S22 measurements are less accurate because the power level from network analyzer source that probes the DUT output is approximately plus 5 dBm (or about 45 dB below the DUT output signal). When reduced by a DUT return loss of perhaps 20 dB the return signal is now 65 dB below the DUT carrier output and is difficult to select and measure accurately. The problem is aggravated when testing a DUT with a very good return loss of more than 20 dB.
Another prior method found in a Japan Radio Corporation (JRC) proposal for a high-power amplifier tester uses a “N by 2” switch matrix to multiplex N DUTs into two measuring ports. One port is connected to a vector network analyzer (VNA) for “hot” s22 injection measurements. The other port is connected to a spectrum analyzer and power meter for spectrum harmonics and power measurements. The switches that are required to switch the DUT output signal between these ports need to be high-power switches and are subject to “hot-switching” situations leading to early failure.
What is needed is a combination of essential power amplifier measurement functions and measurement systems self-test capability into one RF circuit without the need for high-power RF switches or DUT disconnections providing for high reliability, high repeatability, low costs, and high accuracy.